首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   103104篇
  免费   1093篇
  国内免费   1728篇
  2024年   23篇
  2023年   143篇
  2022年   316篇
  2021年   642篇
  2020年   380篇
  2019年   473篇
  2018年   12161篇
  2017年   10933篇
  2016年   7849篇
  2015年   1319篇
  2014年   1131篇
  2013年   1168篇
  2012年   5180篇
  2011年   13611篇
  2010年   12473篇
  2009年   8653篇
  2008年   10289篇
  2007年   11758篇
  2006年   604篇
  2005年   790篇
  2004年   1199篇
  2003年   1234篇
  2002年   956篇
  2001年   404篇
  2000年   302篇
  1999年   148篇
  1998年   89篇
  1997年   116篇
  1996年   97篇
  1995年   65篇
  1994年   59篇
  1993年   77篇
  1992年   84篇
  1991年   88篇
  1990年   57篇
  1989年   42篇
  1988年   57篇
  1987年   41篇
  1986年   24篇
  1985年   36篇
  1984年   41篇
  1983年   32篇
  1982年   17篇
  1975年   13篇
  1974年   13篇
  1973年   13篇
  1972年   248篇
  1971年   283篇
  1965年   19篇
  1962年   24篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
In this paper we propose that the internal bracketing of a word with more than two morphemes is reflected in the phonetic implementation. We hypothesize that embedded forms show more phonetic reduction than forms at higher structural levels (‘Embedded Reduction Hypothesis’). This paper tests the prediction of the Embedded Reduction Hypothesis with triconstituent compounds. The analysis of the durational properties of almost 500 compound tokens shows that there is a lengthening effect on the non-embedded constituent, and a shortening effect on the adjacent embedded constituent. Yet, this predicted effect of embedding interacts with other lexical factors, above all the bigram frequency of the embedded compound. At a theoretical level, these effects mean that the durational properties of the cross-boundary constituents are indicative of the hierarchical structure and of the strength of the internal boundary of triconstituent compounds. Hence, morphological structure is reflected in the speech signal.  相似文献   
202.
203.
204.
205.
206.
The influence of moulded hay (Alternaria alternata, Epicoccum nigrum, Mucor racemosus, Ulocladium chartarum) and the efficiency of Vitamin B1 substitution to cope these effects on rumen protozoa was investigated using the longterm rumen simulation technique (RUSITEC) for about 25 days. Moulded hay affected medium-sized protozoa to a different extent (Alternaria alternata: ?16 %, Epicoccum nigrum: ?27 %, Mucor racemosus: ?9 %, Ulocladium chartarum: +2 %). The vitamin B1 substitution had positive effects during the feeding of Mucor racemosus and Ulocladium chartarum.  相似文献   
207.
An isolated rat liver was perfused with deoxynivalenol (DON) at a dose of 3 mg in a recirculating perfusion system. To identify glucuronide conjugates equal amounts of bile samples, perfusate and liver homogenates were incubated with and without (control) a β-glucuronidase preparation and analyzed by thin layer chromatography and capillary gas liquid chromatography — chemical ionization mass spectrometry. A total of 40.4% of the administered dose of DON was found to be conjugated with glucuronic acid (perfusate 20.4%, bile 19.2%, liver 0.8%), while only 1.3% of the parent DON (perfusate 1.1%, bile 0.2%) was detected. The cleavage of DON-glucuronide was demonstrated by incubating DON-glucuronide containing bile samples with intestine contents under anaerobic conditions.  相似文献   
208.
209.
While only two gamma-crystallins have been identified in the human eye lens, molecular studies indicate that the human gamma-crystallins are encoded in a multigene family comprising at least seven closely related members. Sequence analysis of five of these genes has suggested that three (gamma 1-2, G3, and G4) are potentially active, while two (G1 psi and G2 psi) correspond to closely related pseudogenes. Here we report on the detailed structure of a sixth gamma-crystallin gene, G5, and our results obtained with transient expression assays to characterize both the promoter activity and translation products of five members of the gene family. We show that 5'-flanking sequences of G1 psi and G2 psi lacked detectable promoter activity, while the corresponding sequences of G3, G4, and G5 were able to direct high levels of expression of the bacterial chloramphenicol acetyltransferase gene in primary lens epithelia, but not in cultures of nonlens origin. Detailed sequence comparisons indicated that active genes contained several conserved sequence tracts 5' of the TATA box which may constitute functional elements of a lens-specific gamma-crystallin promoter. Expression of the gamma-crystallin coding sequences from the human metallothionein IIA promoter in nonlens cells facilitated characterization of the polypeptides encoded by individual gamma-genes and, in future studies, should permit comparison of these proteins with distinct gamma-crystallins in the human lens.  相似文献   
210.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号